1. Field of the Invention
The present invention relates to syntheses and utilization of new copper compounds as precursors for chemical vapor deposition to obtain high-quality copper films.
2. Description of the Prior Art
Chemical vapor deposition (CVD) processes have several advantages over physical vapor deposition (PVD) processes, such as the ability of conformal coverage and the possibility of selective deposition, to deposit copper and other metal films. To fabricate desirable materials by CVD processes, it is important to identify precursors which satisfy several requirements. The precursors should be vaporized easily and be thermally, stable at the temperatures at which vaporization occurs and yet can deposit desirable films at low, substrate temperatures.
The need for high performance interconnection materials increases as device feature sizes shrink and device density increases. Copper is expected to provide an alternative to CVD-aluminum or CVD-tungsten for metallization of ultra large scale integrated (ULSI) devices due to its low resistivity (1.67 xcexcxcexa9cm for Cu, 2.65 xcexcxcexa9cm for Al and 5.7 xcexcxcexa9cm for W), high electromigration resistance and high melting point (1083xc2x0 C. for Cu, 660xc2x0 C. for Al and 3410xc2x0 C. for W). Low interconnect resistivity allows for faster devices.
Copper CVD precursors arc divided into two groups, i.e., Cu(I) and Cu(II) complexes. The precursors in the former group are quite volatile and show low deposition temperatures, but are highly, sensitive to heat and oxygen. The latter precursors are rather stable, but are isolated as solids with high melting points and thus require high deposition temperatures. It is not uncommon that impurities such as carbon or oxygen are incorporated during the thermal CVD process when using certain organometallic precursors. For instance, (xcex75-C5H5)Cu(PMe3) and (tert-BuO)Cu(PMe3) produce copper films via thermal decomposition reactions leading to incorporation of impurities. To avoid such a problem, it is necessary to tailor an organocopper precursor to deposit copper without decomposition of the ligands.
(hfac)CuL, where hfac=1,1,1,5,5,5-hexafluoro-2,4-pentanedionate and L=Lewis base, have been the most studied copper precursors to date because they can deposit copper via thermal disproportionation reaction. Especially (hfac)Cu(tmvs), where tmvs=trimethylvinylsilane, has attracted much attention since it is a liquid with reasonably high vapor pressure. Other copper compounds such as (hfac)CuL, where L=1,5-cyclooctadiene (COD), alkyne or trialkylphosphine, are either solids or liquids with a low vapor pressure. Although (hfac)Cu(tmvs) has been the most utilized copper precursor, its stability is not satisfactory for the selective growth of copper films with reproducibility (L. H. Dubois, et al., J. Electrochem. Soc., 1992, 139, 3295). In addition, a study (V. M. Donnelly, et al., Vac. Sci. Technol. A, 1993, 11, 66) demonstrated that the chemical vador deposition reaction of (hfac)Cu(tmvs) under ultra high vacuum conditions produced contamination by carbon and fluorine in the deposited films. This implies a possibility of fluorine contamination during the deposition process under certain conditions. Copper compounds of fluorinated (xcex2-diketonates other than (hfac)CuL, such as (fod)CuL, where fod=2,2-dimethyl-6,6,7,7,8,8-heptafluoro-3,5-octanedionate (fod), or (tfac)CuL, where tfac=1,1,1-trifluoro-2,4-pentanedionate, were reported not to exhibit sufficient thermal stability to be used as CVD precursors (K. M. Chi, et al., J. Organomet. Chem., 1993, 449, 181). Therefore, a precursor with high volatility and stability, which contains no fluorinated ligands, is more desirable for the deposition of copper by CVD.
Copper compounds of acetoacetate derivatives which contain no fluorinated ligands were reported as CVD precursors. They were reported to be volatile and to deposit copper films at low substrate temperatures (H. Choi, et al., U.S. Pat. No. 5,441,766). Cu(II) acetoacetate derivatives in the report were found to be attractive since they were volatile without employing fluorinated ligands and deposited copper films at temperatures below 200xc2x0 C. However, they were solids with high melting points and were incapable of selective deposition of copper. On the other hand, the Cu(I) acetoacetate derivatives deposited copper films at relatively low temperatures via disproportionation reaction. However, few are practical for use as CVD precursors since they are either solids or liquids with a low vapor pressure or they have an extremely low thermal stability (i.e. their decomposition temperature is within a few degrees of their vaporization temperature). A limited claim was made to the alkylphosphite family of Cu(I) acetoacetate precursors demonstrated to deposit copper at low temperatures (H. Choi, Korean Patent Application No. 1998-32069). This is an expansion of those claims to include other recent works presented by Choi et al. (H. Choi, et al. Chem. Mater. 1998, 2326).
The object of the present invention is to provide new Cu(I) CVD precursors which contain no fluorinated ligands and are capable of depositing high-quality copper at low deposition temperatures.
The precursors according to the invention include: (R3COOCR2COR1)Cu+1{L}x, where x is 1, 2 or 3, L is a neutral ligand which is a phosphine, phosphite or an unsaturated hydrocarbon, and R1 and R3 are each independently C1-C9 alkyl or aryl groups and R2 may be H, F or C1-C9 alkyl or aryl groups, wherein R3 may also be an alkylsilane group, {xe2x80x94Si(R4)(R5)(R6)}, wherein R4, R5 and R6 independently may be C1-C9 alkyl or aryl or alkoxy (xe2x80x94OR where R is C1-C9 alkyl or aryl) groups attached to silicon. The precursors in the present invention, which are low melting solids or distillable liquids with high volatility and thermal stability, can be vaporized without decomposition and used to deposit high-quality copper films. The improved stability of the copper compounds in the present invention enables them to reproducibly produce selective copper films on metallic or electrically conductive surfaces.
Further objects and advantages of the invention will become apparent through reading the remainder of the specification.
According to the invention, the general formula of the organocopper precursor is (R3COOCR2COR1)Cu+1{L}x 
where
x is 1, 2 or 3;
R1 and R3 are each independently C1-C9 alkyl or aryl groups and R2 may be H, F or C1-C9 alkyl or aryl groups, wherein R3 may also be an alkylsilane group, {xe2x80x94Si(R4)(R5)(R6)}, wherein R4, R5 and R6 independently may be C1-C9 alkyl or aryl or alkoxy (xe2x80x94OR where R is C1-C9 alkyl or aryl) groups attached to silicon; and
L is a neutral ligand which can be a phosphine or phosphite ligand, {P(R7)(R8)(R9)} wherein R7, R8 and R9 are each independently hydroxy or C1-C9 alkyl or aryl or alkoxy (xe2x80x94OR where R is C1-C9 alkyl or aryl) groups wherein if at least one of R7, R8 or R9 groups is an alkoxy group the electron donating ability of oxygen in the phosphite ligand strengthens the bond between the Cu and the phosphite ligand resulting in enhanced stability of the compound.
The neutral ligand, L, may also be an unsaturated hydrocarbon described as (R10)(R11)xe2x80x94Cxe2x95x90Cxe2x80x94(R12)(R13) containing at least one carbon-carbon double bond, wherein R10, R11, R12 and R13 are each independently H, F, C1-C9 alkyl or aryl or an alkylsilane group, {xe2x80x94Si(R14)(R15)(R16)}, wherein R14, R15 and R16 independently may be C1-C9 alkyl or aryl or alkoxy (xe2x80x94OR where R is C1-C9 alkyl or aryl) groups attached to silicon, and any combination of R10, R11, R12 or R13 may be joined together to form at least one C4-C16 cycloaliphatic ring containing at least one carbon-carbon double bond.
The neutral ligand, L, may also be an unsaturated hydrocarbon described as (R17)xe2x80x94Cxe2x89xa1Cxe2x80x94(R18) containing at least one carbon-carbon triple bond. wherein R17 and R18 are each independently H, F, C1-C9 alkyl or aryl or an alkylsilane group, {xe2x80x94Si(R14)(R15)(R16)}, wherein R14, R15 and R16 independently may be C1-C9 alkyl or aryl or alkoxy (xe2x80x94OR where R is C1-C9 alkyl or aryl) groups attached to silicon, and R17 and R18 may be joined together to form at least one C4-C16 cycloaliphatic ring containing at least one carbon-carbon triple bond.
The charged ligand, (R3COOCR2COR1), is an acetoacetate derivative, and is most preferably 1BuCOOCHCOCH3 or tert-butylacetoacetate. The precursor can be synthesized by the following method:
Reaction of sodium acetoacetate derivative with the neutral ligand adduct of cupurous chloride.
CuCl+x{L}xe2x86x92{L}x.CuClxe2x80x83xe2x80x83(1)

The Cu(I) compounds, (acetoacetate derivative)Cu+1(neutral ligand), synthesized in the manner described above, are obtained as distillable liquids or low melting solids with high volatility and exhibit improved thermal stability and deposition characteristics. It is important to judiciously choose the appropriate ligand as a Lewis base to achieve higher thermal stability of the precursor. The improved stability of the copper compounds in the present invention enables them to produce selective copper films over a wide temperature range. The copper films thus formed using the present invention are free from carbon-, oxygen- or fluorine-containing impurities since there are no fluorine atoms in the precursor and the films are deposited via disproportionation reaction instead of a thermal decomposition reaction.
The precursors obtained in the manner described above were subjected to a chemical vapor deposition apparatus comprising a precursor vessel, a heated Pyrex reactor and a vacuum system to produce copper thin films. The vaporized precursor is injected into the reactor with or without hydrogen gas while the precursor vessel is maintained in the temperature range of 15-100 xc2x0 C. When the precursor reaches the substrate, a thermally induced disproportionation reaction deposits copper on the substrate. Silicon (Si), or coated silicon (SiO2/Si or TiN/Si) wafers are used as substrates, but any substrate suitable for the CVD process may be used. Depositions are conducted over the temperature range of 100-300 xc2x0 C. The reactor is maintained at 0.1 to 10 mmHg during the deposition reaction, and the deposition rate is dependent upon the reaction conditions used.
The compounds in the present invention are suitable for the production of high-purity copper films due to the fact that there are no fluorine atoms in the precursors and that the deposition of copper occurs via disproportionation reaction as shown in eq. 3. The resulting volatile Cu(II) acetoacetate derivative and neutral ligand evolved from the disproportionation reaction are passed out of the deposition zone intact. 
Another advantage of the present invention is that it allows selective deposition on metallic or electrically conductive surfaces with wide temperature window. Copper films were deposited on Si or TiN/Si wafers as low as 120xc2x0 C. while no deposition was observed on SiO2/Si at 200xc2x0 C. The favored deposition of copper on Si or TiN/Si surfaces can be explained by the catalytic effect of metallic or electrically conductive surfaces to promote the disproportionation of the Cu(I) compounds. Therefore, the selectivity is expected to improve with the thermal stability of the precursor. The improved thermal stability of the precursors in the present invention is very important for the selective deposition of copper with reproducibility.
The thermal stability of Cu(I) acetoacetate derivatives in the present invention was improved remarkably by employing such materials as trimethylphosphite (TMP), 1,5-dimethyl-1,5-cyclooctadiene (1,5-DMCOD) or bistrimethylsilylacetylene (BTMSA) as new ligands so that the resulting adducts can be used as practical CVD precursors.
Scanning electron microscopy (SEM) image of the deposited copper films using the present invention showed good surface morphology and step coverage on vias of ULSI substrates. No impurities such as carbon or oxygen were detected from the X-ray photoelectron spectra (XPS) of the deposited films. The resistivities of the as-deposited films ranged from 1.8 to 2.5 xcexcxcexa9cm.
The present invention will be illustrated in greater detail by way of following examples. The examples are presented for illustrative purpose only and should not be construed as limiting the invention, which are properly delineated in the claims.
All reactions and subsequent manipulations involving organometallic reagents were performed under an inert atmosphere (for example, helium, argon or nitrogen) using Schlenk-type glassware and glove box techniques. All reagents were purchased from Aldrich Chemical Co. (Milwaukee, Wis.). All solvents were purchased from Baxter Healthcare Co. (Muskegon, Mich.) and freshly distilled from Na under nitrogen. Trimethylphosphite, 1,5-dimethyl-1,5-cyclooctadien, bistrimethylsilylacetylene and tert-butylacetoacetate (Hbtac) were freshly distilled under nitrogen. Infrared spectra were recorded on either a BioRad FTS60A FT-IR spectrometer or a Perkin Elmer 1600 Series FT-IR spectrometer.